The present invention disclosed herein relates to a photonics device and a method for fabricating the same, and more particularly, to a hybrid laser diode for single mode operation and a method for fabricating the same.
The present invention has been derived from research undertaken as a part of the information technology (IT) development business by the Ministry of Information and Communication and the Institute for Information Technology Advancement of the Republic of Korea [Project management No.: 2006-S-004-02, Project title: silicon-based high-speed optical interconnection IC].
Hybrid laser diodes that employ silicon and III-V compound semiconductors are acknowledged as promising light sources in the field of photonics, a fusion of optical and electronic device technologies. When applying hybrid laser diodes as light sources for data transmission, it is desirable to realize single mode operation laser diodes to improve transmission quality.
As widely known, a laser diode includes an active medium, an energy pumping source, and a resonator. The active medium, also referred to as a gain medium, is a medium in which electron population inversion induced by the pumping mechanism occurs. In a hybrid laser diode, a quantum-confined active layer typically formed of group III-V compound semiconductors is used as the active medium. The energy pumping source supplies energy to induce electron population inversion, which is realized through electrical energy supplied from an electric power supply to the hybrid laser diode. The resonator is configured to provide an optical path through which light with a specific wavelength can reciprocate such that light of the same phase can be amplified by the active medium.
In a typical laser diode, the resonator may be realized through an external resonator formed outside the laser diode or through a diffraction grating. When an external resonator is employed, not only is the size of the device increased, but having to optically connect the resonator presents technical challenges. Accordingly, the use of external resonators is restricted mostly to laser diodes used as variable wavelength light sources.
With the use of a diffraction grating, while the above technical hurdles relating to optical connections can be obviated, it is not easy to realize a single optical mode. That is, laser diodes using diffraction gratings can largely be categorized into distributed Bragg reflector lasers (DBR lasers) and distributed feedback lasers (DFB lasers). While the DBR laser characteristically has at least one distributed Bragg reflector (DBR) disposed outside the active medium to provide periodic changes to the effective refractive index within a waveguide, the DBR laser is more complicated to fabricate than the DFB laser.
The DFB laser is one type of laser diode with its active region directly forming the diffraction grating, and is characterized by its bumped diffraction grating formed on the entire region of the resonator. In this case, the diffraction grating formed provides optical feedback through Bragg scattering. While simpler in terms of fabrication process than the DBR laser as stated above, because the DFB laser provides dual mode oscillation, it cannot easily realize a single mode operation.
Because hybrid laser diodes are fabricated using wafer bonding techniques, surfaces for surface bonding should have a root-mean-square (rms) roughness of below 3 Å. However, as described above, when a diffraction grating for the resonator is bumped, it is difficult to maintain surface conditions to satisfy the above roughness requirement. Moreover, because silicon or InP with high refractive indices is used as materials for diffraction gratings in typical hybrid laser diodes, excessive optical feedback and resultant light distribution localization are manifested. Thus, it has been difficult to use single mode operation technology employing typical diffraction gratings as methods for forming high output single mode hybrid lasers.